The present invention concerns pushrods for the valve train of an internal combustion engine and more particularly pushrods formed of composite materials.
It has heretofore been proposed that internal combustion engine valve train pushrods be constructed of a composite material such as epoxy resin with embedded strands of lightweight fibers such as graphite, glass or Kevlar (TM). Such composite pushrods are described in U.S. Pat. No. 4,453,505, and U.S. Pat. No. 5,154,146.
Composite pushrods have been known to be produced by being pultruded as described in detail in U.S. Pat. No. 4,296,060 and the aforementioned U.S. Pat. No. 5,154,146. Composite pushrods so constructed are lighter and quieter than conventional steel pushrods.
The ends of the pushrods must engage the driving and driven components in the valve train and hence are provided with spherically shaped tips of a harder material such as steel or ceramic. The tips have heretofore been configured of solid pieces which are adhesively bonded to each end of a composite rod forming the main body of the pushrod. These tips are relatively costly and add significantly to the mass of the pushrod.
U.S. Pat. No. 4,186,696, Japanese Patent Publication 57-13204 dated Jan. 23, 1982, and Japanese Patent Publication 59-155516 dated Sep. 4, 1984, show composite pushrods having various forms of these solid tips affixed to either end.
One problem with the pultruded tube construction is the failure by cracking along the boundaries between fibers. This failure mode is described in U.S. Pat. No. 5,154,146. Brooming, i.e., the mushrooming of the ends, also may occur due to compression of the end of the composite rod or tube.
The tip constructions heretofore have caused at least small sections of the end of the composite tube which are unconfined by the tip to be stressed in compression such as to allow the failure by cracking and/or brooming of the embedded fibers.
Accordingly, it is an object of the present invention to provide an improved pushrod for an internal combustion engine valve train in which the total mass of the pushrod including the tips is minimized.
It is a further object of the present invention to prevent pushrod failure by cracking along the fiber boundaries and/or brooming of the ends.
It is a further object of the present invention to provide such a pushrod in which the cost of manufacture is also minimized.